For a large number of gas analysis situations, it is required to pursue several reactions simultaneously or at least substantially simultaneously, and to measure them with one and the same detector.
The hitherto known devices for such multiple analyses of gases all operate with an optical-fiber system. GB-A 2,016,679, e.g., discloses a chemiluminescence gas analyzer with two reaction chambers, in which light emitted from two reaction chambers is in each instance transmitted by means of a mechanical interrupt ("chopper") to one of the branches of a Y-shaped light-conductor which conducts the light to a single, central photodetector. In order to maintain the necessary level of quality, large-cross-section light conductors are necessary, which are extraordinarily expensive.